Boy racer: Jann Mardenborough, who beat 90,000 virtual drivers to gain his place in the GT Academy, at the start of the Dubai 24 Hour race. Photograph: Andy Hall for the Observer

Jann Mardenborough grew up dreaming of driving racing cars. It was an infatuation that had begun with the gift of a Matchbox toy as a baby, but which he pursued with such quiet intensity that even his father Steve discovered only a year ago that motor racing – not football – was Jann's first love. Jann was quiet. To his mother Lesley-Anne he was "not particularly outgoing and quite a home boy". Often too shy to answer the front door, he'd spend time in his bedroom, where he played video games. Yet this reserved, awkward teenager from Cardiff had a big surprise in store for his parents.

At eight, Jann thought he might have a chance of making it as a racing driver. Steve, an ex-professional footballer, had taken him to a kart circuit, and before long the owner took notice and told Steve his son was a natural. But finance proved the stumbling block. The local track closed down and the nearest alternative was in Bristol. "I stopped when I was 11," says Jann, "because it got too expensive."

He returned quietly to his bedroom, where he took to the next best thing – virtual racing on the video game Gran Turismo. It was the perfect release for the racing-obsessed teen: a singular pursuit offering a test of individual skill in which he could lose himself.

In the middle of 2011, Mardenborough had entered an online competition on Gran Turismo 5 that offered one final shot at the real thing. Out of 90,000 other virtual racers, he made it into the top eight in Europe and won the chance to test himself against other gamers in a real car at Brands Hatch. That he had kept it to himself for so long was entirely in character for a boy who did not like to make a fuss. "At that point we had no idea what it was," admits Steve.

Seven months later, in January this year, Mardenborough, who'd never set foot in a racing car, was at the wheel of a serious piece of kit in the Dubai 24 Hour race – and at the beginning of what appears to be a very exciting career.

The video-game franchise in which Mardenborough began his journey, Sony's Gran Turismo, was originally designed by Japan's Kazunori Yamauchi in 1997. In an industry often (unfairly) accused of infantilism, Gran Turismo stands out for its quest to mirror a physical rather than fantastical reality. This is a racing "simulator" and its success (more than 60m sales worldwide) owes everything to how well it measures up to the real thing. Its sports cars may be but virtual creations, yet everything about them is designed to behave as closely as possible to the genuine article.

The level of accuracy now available in computer modelling means Formula One drivers, as a matter of course, do laps on simulators in preparation for races. Lewis Hamilton himself admitted to learning tracks during his rookie F1 year playing PlayStation with his brother.

Visually, the game is stunning. In cockpit mode, with a virtual dashboard at the bottom of the screen, the bonnet and track stretching to the fore and the claustrophobic confines of the interior rendered on the periphery, there is little or no conscious need to suspend disbelief. The pedal goes down and players are "in" the game – unconsciously leaning into corners and breathless while trying to thread through a pack of competitors.

But however accurately the game mimics reality, there is one crucial difference: simulations still lack movement – the sensation of the car reacting, grip felt through the seat of the pants, acceleration that compresses the body, and the forces generated in cornering.

Sensing a marketing opportunity, Sony teamed up with Nissan to form the GT Academy in 2008. It was a one-off project created to answer a simple question: could you take a gamer and put them in a real racing car? A 23-year-old Spaniard, Lucas Ordoñez, who was just beginning a business degree, won the online and then real-world challenge. After intensive training, he raced as one of a team of drivers in the 2009 Dubai 24.

With the marketing objectives achieved, it could have ended there. Except, much as he was just a gamer, Ordoñez was good. "I'm not a nervous guy, but I was physically sick with worry that we were sending this guy out to his death," said Nissan's Darren Cox.

But the way the driver dealt with a problem calmed his nerves. "I remember hearing the radio: 'Left rear puncture, coming into the pits; please change left rear.' He's in a 400 horsepower Nissan 350Z, he's got a crash helmet on, he's got the car moving around underneath him, but he's calm. And at that point I knew we had something," says Cox.

The programme was extended to see if this unorthodox method could uncover further talent. French gamer Jordan Tresson won a GT Academy place in 2010 and Ordoñez himself went on to race for the professional Signature Nissan team, taking a podium at sports car racing's most important meeting, the Le Mans 24 Hours, in 2011. From this came the concept of a car driven only by computer gamers entering this year's Dubai 24. Two new candidates were needed to be brought up to speed and the academy opened its online competition again. Which was how Jann Mardenborough found it.

The transition from computer-generated racing to hard, cold, dangerous steel ought to be both difficult and potentially terrifying, yet for Mardenborough it was instinctive: "It felt completely normal," he says. How to read racing lines – correct entrances and exits to corners; hand-eye co-ordination and a visual sense, plus the ability to look ahead of the car into breaking zones, had all been learned in the bedroom. "I'd never power-steered a car before," says Mardenborough. "I had only ever done it in a game. I was controlling it just with the throttle and it was completely natural to me."

He passed the test at Brands Hatch and later, at Silverstone, beat 11 other finalists to the place as a GT Academy driver. "My mouth was hurting because I was grinning from ear to ear so much," he says. "I met Bob [Neville], my team manager, straight after. That was the moment I realised I was a racing driver." Mardenborough was placed on a driver-development programme at Silverstone. In six months he and the winner of the US GT Academy, Bryan Heitkotter, gained their international racing licences, a process that normally takes three years.

The gamers are young, malleable and without ego. Even the lack of racing experience has a positive side-effect. Mardenborough's mentor Rob Jenkinson, a former racer himself, was sceptical of the academy concept but became convinced after seeing it in action. He explains that drivers entering through the traditional route have longer to pick up bad habits, sometimes taking years to correct. "With this, in six months we eliminate mistakes," he says. "We make good decisions on their behalf immediately."

What cannot be eliminated is the danger. Accidents now mean more than just hitting the restart button. "I know there's a dangerous side to it, but it didn't really cross my mind," Mardenborough says, despite having rolled the car at a race in Holland.

The Dubai MotorCity circuit forms part of Dubailand, which was to be a vast theme park stretching into the desert, featuring Tiger Woods's first golf-course design. Today sand blows across empty lots and cranes loom over half-finished buildings, exactly as they were in 2008 when the financial crisis stopped the project in its tracks – reminders of the dangers of expecting too much, too soon. It's a lesson not lost on the gamers and their RJN Motorsport team.

Mardenborough bounces through the paddock and pit lane on his toes, ready for the Dubai 24 Hour race. He shares with Hamilton not only the sculpted good looks but the calm self-assurance the McLaren driver displays. There's no sign of the shy teenager. Motor racing is all about focus, and before he steps into the car Mardenborough has it in spades.

For the first part of the race, the crew and drivers are struggling with mechanical gremlins, and tension suffuses the coarse desert air.

Endurance racing is like no other. It is a bewildering assault on the senses. The noise never abates and the cars spread out until there seems to be an endless stream streaking past, the atmosphere thick with the smell of rubber and oil. Each team races flat-out stints interspersed with furiously quick pit stops, looking to eke out tiny advantages that over a full 24 hours can make the difference between winning and losing. Through all this, the overriding aim is to at least finish the race – to see the chequered flag come down – and fortunately the early fears that technical problems might signal game over are dismissed as the car settles down into quick, trouble-free racing through the night and into the morning.

With an hour and a half to go, one driving stint remains and now, in third place, Neville chooses Mardenborough to take the wheel. Having raced so hard for so long, a mistake at this stage would be heartbreaking. The pressure is immense. Mardenborough brings the car home with ease and the team is on the podium.

"When I was 17 or so I was afraid to answer the phone," he tells me afterwards. "I've come a huge, long way." His mother calls it a "fairy story". Perhaps, as the academy opens its doors again on Tuesday to search for further young talent, it is also a fable for the modern age – where video gaming isn't all bad.

Just over two weeks after the race Nissan confirmed Mardenborough as its full-time driver for the season in the Blancpain Endurance Series – a full-scale, six-race, professional racing competition that visits some of the most famous circuits in Europe. It might be the start of something great. "Jann's 20 and there's a very wide sphere ahead of him," says Neville. "We have to just keep the lid on him..."